notes 10-7

October 7, 2009 notes
1) Factors that influence bacterial growth
• Bacteria live in an aqueous environment.
a) Bacterial cell walls make bacteria more resistant to osmotic pressure than eukaryotic cells.
b) If cell wall is compromised then the bacteria are not resistant to osmotic stress than eukaryotic cells.
• Cell envelope stuff protects bacteria from osmotic pressure.
a) What happens to E. coli if you put it in distilled water?
 When they are treated with penicillin it weakens the cell wall causing the E. coli to blow up, they also keep elongating but do not split because they are unable to create the new pieces for the cell wall.
b) There is some turnover in cell envelope components.
• Osmotic pressure and availability of water
a) Water availability
 Distilled water= 1.0
 Blood= 0.95—E. coli prefers this water availability & virtually all bacteria that live in people
 Sea water= 0.90
 Honey= 0.80
1) Halophiles: bacteria that live at low water availability levels.
 By having very high solute concentration inside cell, halophiles are able to pull water into cell even when in very water-poor environments.